Magnetic resonance imaging (MRI) is an imaging method which magnetically excites nuclear spins of a patient placed in a static magnetic field with an RF signal at the Larmor frequency to reconstruct an image using an NMR (nuclear magnetic resonance) signal resulting from the excitation.
In magnetic resonance imaging, when frequency of a transmitted RF pulse increases, an RF magnetic field in the patient becomes non-uniform. The non-uniformity of the RF magnetic field is also referred to as B1 non-uniformity. Thus, it is important to correct the B1 non-uniformity.
For example, a B1 correction method has been proposed which determines amplitude and phase of an RF transmit pulse based on aspect ratio. Also, a method is known which collects a B1 map by changing the amplitude and phase of an RF transmit pulse and thereby determines the amplitude and phase of the RF transmit pulse.
However, an MRI apparatus with high magnetic field strength have come to be developed recently. Consequently, the frequency of RF pulses has become greater, making it difficult to resolve the B1 non-uniformity even if an RF pulse is transmitted using the amplitude and phase determined based on aspect ratio as is conventionally the case. On the other hand, when collecting a B1 map by changing the amplitude and phase of an RF pulse as is conventionally the case, there are problems of increased imaging time and difficulty to determine B1 non-uniformity.
Thus, there is demand for a magnetic resonance imaging apparatus which can further improve B1 uniformity in a simple way.